The Michoacan stream salamander exhibits some highly unusual and distinct features, indicative of its evolutionary distinctiveness. Based on studies of its DNA and proteins, it is thought to be one of the most distinct species of Mexican mole salamander. This is a fairly large species of salamander, reaching a total length of around 170 mm, with a tail that measures about 75 mm. Most individuals do not metamorphose, but local people report that some do leave their watery habitats for a life in a different form on the land. The species may be threatened by the pollution and desiccation of its breeding streams, which is resulting from current water extraction activities.

Urgent Conservation Actions

Conserve and restore the forests surrounding the city of Morelia and those in the vicinity of Patzcuaro

The family Ambystomatidae is also referred to as the mole salamanders because many live in burrows for much for their lives. They are found only in North America (from Canada down to Mexico), the majority (as is occasionally the case for the Michoacan stream salamander) metamorphose from aquatic larvae to become terrestrial adults that are rarely seen except in the breeding season, when they migrate to ponds to mate and deposit eggs.

Evolutionary Distinctiveness

Order: Caudata

Family: Ambystomatidae

The family Ambystomatidae or “the mole salamanders” is included within the four earliest or most primitive family lineages of the order “Caudata” (the salamanders), diverging from all other salamanders in the Early Cretaceous period over 140 million years ago, around five million years before the koala and dolphin lineages diverged from their common ancestor. The small number of species that represent the genus Ambystoma are highly evolutionarily distinct members of both the salamanders and the amphibians as a whole.

The Michoacan stream salamander exhibits some highly unusual and distinct features, indicative of its evolutionary distinctiveness. Based on studies of its DNA and proteins, it is thought to be one of the most distinct species of Mexican mole salamander and may be composed of more than one species. Ambystoma ordinarium is capable of reaching sexual maturity in its neotenous form, retaining its aquatic larval characteristics such as fins and gills throughout its life. However, it is also able to metamorphose into the adult form and live a terrestrial life. Although the species has been little-studied, there are a couple of theories that may explain why some populations of the blunt-headed salamander do not metamorphose. One idea is that the production or effectiveness of the hormone thyroxine is compromised, either by the species living in water bodies containing insufficient iodine (which is required in the manufacture of thyroxine by the body) or in water temperatures that are too cold for the thyroxine to be effective. This impacts on the development of the species and sexually mature adults never develop adult characteristics but remain in the larval form. A second theory suggests that species evolving in pools surrounded by hostile terrestrial environments develop aquatic lives to obviate the need to exit the relative safety of their watery home. This is a common trait in species that inhabit high-elevation ponds. Since the Michoacan stream salamander inhabits various water bodies across its range, and is able to disperse between them in its metamorphosed form, it is possible that the conditions in some of these water bodies are not conducive to metamorphosis.

Description

An Ambystomatid, or mole salamander, occurring on the northeastern parts of the state of Michoacan, Mexico at an elevation of 2,200 meters. Mole salamanders are medium to large, stocky amphibians, usually measuring between 90 to 350mm from the tip of the nose to the end of the tail, which salamanders retain throughout their life. Males are often larger than females, partly due to their longer tails. Ambystomatids generally exhibit both aquatic “neotenic” larval (or aquatic and permanently juvenile in form with external, feathery gills) and terrestrial “metamorphosed” (or ground-dwelling, fully developed adult in form with reduced gills) stages in their wild populations. Ambystomatids are often boldly patterned as adults, with well-developed “costal” grooves (successive vertical grooves along the sides of the body), especially the metamorphosing varieties. They have a rather flattened body with a wide, flattened head, a large mouth and smooth skin with many glands. The tail is roundish or laterally compressed. During the breeding season, males have a very swollen cloacal zone (the region around the reproductory and excretory opening in amphibians located underneath the base of the tail).

The Michoacan stream salamander has both neotenic and fully developed terrestrial (or ground-dwelling) populations. Neotenic populations retain their gills and fins throughout life, whereas metamorphosed individuals develop adult traits, such as a lack of gills, functioning lungs, eyelids and no fins. This is a fairly large species of salamander, reaching a total length of around 170 mm with a tail that measures about 75 mm. The skin of the head is slightly corrugated and pitted. Eleven costal grooves are visible in the skin along either side of the body and the limbs are rather short. The colouration of this species is uniform greyish-black and the tips of the digits are blackish-brown. The neotenic forms are small, reaching a total length of around 90 mm and possess a caudal fin along the tail that does not continue into a dorsal fin along the back.

Ecology

The Michoacan stream salamander is a species that is polymorphic for metamorphosis. This means that it may metamorphose into the adult form (losing its gills and fins and becoming capable of living out of water) or it may remain in its aquatic larval form throughout its life, reaching reproductive maturity without developing other adult characteristics. This would be akin to a tadpole being able to breed without ever turning into a frog. Most individuals do not metamorphose, but local people report that some do leave their watery habitats for a life in a different form on the land. Most Michoacan stream salamanders spend their time in streams, where they can be found all year long. Regardless of whether they undergo metamorphosis or not, all forms breed in streams.

Once the eggs are laid in water they are left to develop with no further participation by either parent. This species does not exhibit parental care.

Habitat

Abundant in streams in pasture land, as well as in forests, although it appears not to be forest-dependent. Those individuals that do metamorphose into the adult form become capable of a ground-dwelling lifestyle, and probably spend most of their time on land in pine and fir forests. They appear to favour clear water, but have been found in very cloudy water, and behind small dams constructed for livestock.

Distribution

Northeastern parts of the Mexican state of Michoacan, from Morelia to the south and east to El Mirador and nearby localities. It occurs at altitudes exceeding 2,200m above sea level.

Although the Michoacan stream salamander is confined to a small area, it was found to be common in 1999 when high population numbers where discovered in many localities, with many of these populations appearing to be stable. More recent surveys are required in order to detect any drastic declines in this species.

Population Trend

The IUCN Red List of Threatened Species indicates that the Michoacan stream salamander’s total population size is generally in decline.

Status

Listed as Vulnerable in the IUCN Red List of Threatened Species because its extent of occurrence is less than 5,000 km sq. and its area of occupancy is less than 500 km sq., its distribution is severely fragmented, and there is continuing decline in the extent and quality of its forest habitat in northeastern Michoacan.

Threats

The species may be threatened by the pollution and desiccation of its breeding streams, which is resulting from water extraction. Introduced predatory fish might also be a problem in some of the water bodies that this species inhabits. Forest loss appears not to be a problem for this species, since it is also found in pasture land. Overall, it appears that this species is not very seriously threatened although there is still cause for concern because of the damage being inflicted upon many areas of its habitat and the fragmented nature of its distribution.

Conservation Underway

The Michoacan stream salamander occurs in the Bosencheve National Park and is protected under the category Pr (Special Protection) by the Government of Mexico.

Conservation Proposed

The main priority for the protection of this species in the wild is the conservation and restoration of the forests surrounding the city of Morelia and in the vicinity of Patzcuaro.

Captive breeding for potential re-introduction of the Michoacan stream salamander should also be investigated and attempted. This would involve creating a breeding colony of this species maintained outside its natural habitat, giving rise to individuals from that species that are sheltered from problems associated with their situation in the wild. This can be located within the species’ range or in a foreign country that has the facilities to support a captive breeding programme for that species. It might be possible to breed the Michoacan stream salamander in captivity and reintroduce them into the wild, in which case captive animals could be a source of new individuals to repopulate natural habitats whilst its ecosystem is restored and an environmental management plan is developed for this species and its habitat.